Introduction to Visual Basic and Visual C++ Arithmetic Expression. Arithmetic Expression. Using Arithmetic Expression. Lesson 4.

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1 Introduction to Visual Basic and Visual C++ Arithmetic Expression Lesson 4 Calculation I154-1-A Peter Lo I154-1-A Peter Lo Arithmetic Expression Using Arithmetic Expression Calculations can be performed with variables, constants, properties of certain objects, and numeric literals Do not use strings in calculations Values from Text property of Text Boxes Are strings, even if they contain numeric data Must be converted to a numeric data type before performing a calculation I154-1-A Peter Lo I154-1-A Peter Lo

2 Using Calculations in Code Perform calculations in assignment statements What appears on right side of assignment operator is assigned to item on left side Assignment operators = assign += add and assign -= sub and assign *= multiply and assign /= divide and assign \= integer division and assign ^= power and assign &= append and assign E.g. a = a + 2 a += 2 a = a - 2 a -= 2 a = a * 2 a *= 2 a = a / 2 a /= 2 a = a \ 2 a \= 2 a = a ^ 2 a ^= 2 a = a & 2 a &= 2 Type Conversion TryParse and Convert I154-1-A Peter Lo I154-1-A Peter Lo Data Type Conversion Using the Convert Class String Integer Convert class: Contains methods for converting numeric values to specific data types Use the dot member access operator to separate the class name from the method name Commonly used methods of the Convert class include: ToDouble ToDecimal ToInt32 ToString I154-1-A Peter Lo I154-1-A Peter Lo

3 How to use Convert Class? Using the TryParse Method TryParse method Exist in every numeric data type s class Used to convert a string to that numeric data type Basic syntax of TryParse method has two arguments: String: string value to be converted Variable: location to store the result If TryParse conversion is successful, the method stores the value in the variable. Otherwise, a 0 is stored in the numeric variable I154-1-A Peter Lo I154-1-A Peter Lo How to Use TryParse Method? Option for Compiler Checking The Visual Basic compiler provides several options for checking your code at compile time. Option Explicit determines whether variables must be explicitly declared. Option Strict determines whether explicit narrowing conversions and late binding are allowed. Option Infer enables type inference for member-level (local) variables. Option Compare specifies the method that is used for string comparisons: binary (case-sensitive) or text (caseinsensitive). I154-1-A Peter Lo I154-1-A Peter Lo

4 Option Explicit When Option Explicit is turned off, you can use any variable name without first declaring it. In VB.NET the Option Explicit is turned on by default for all new projects. All variables are declared before being used. When Option Explicit is turned on, you must declare both var1 and var2 before writing var1 = var2 + 1 Option Strict You must use the statement Option Strict On in projects to ensure that: All variables are declared prior to use Data conversions are not done from a wider type to a narrower type E.g. a decimal number 5.43 is not automatically converted to an integer 5 Option Strict does not allow any implicit conversions from a wider data type to a narrower one or between String and numeric data types. I154-1-A Peter Lo I154-1-A Peter Lo Option Infer Option Infer Off statement ensures that every variable is declared with a data type Option Infer Off warns if a variable declaration does not include a data type Setting for Option Explicit, Option Infer & Option Strict by Configuration Open the project properties dialog box and select Compile tab page. By default: Option Explicit and Option Infer is turned on Option Strict is turned off. I154-1-A Peter Lo I154-1-A Peter Lo

5 Setting for Option Explicit, Option Infer & Option Strict by Programming Rules and Examples of Type Conversion Option statements entered in the General Declarations section I154-1-A Peter Lo I154-1-A Peter Lo Relational Operators Relational and Logical Operators Relational operators are binary they require an operand on both sides of the operator Result of a relational expression will always be Boolean They are evaluated from left to right with no order of operations Compound Decision I154-1-A Peter Lo I154-1-A Peter Lo

6 Logical Operators Used for joining Boolean expressions Not makes a False condition True and vice versa And will yield a True if and only if both expressions are True Or will yield a True if one or the other or both expressions are True Example To test if n falls between 2 and 5: (2 < n ) And ( n < 5 ) A complete relational expression must be on either side of the logical operators And and Or. The following is NOT a valid way to test if n falls between 2 and 5: (2 < n < 5 ) I154-1-A Peter Lo I154-1-A Peter Lo Order of Operations The order of operations for evaluating Boolean expressions is: Arithmetic Operators Parenthesis Exponentiation Division and multiplication Addition and subtraction Relational Operators Logical Operators Not And Or I154-1-A Peter Lo Control Structures Sequence, Selection and Iteration Structure I154-1-A Peter Lo

7 Control Structure Three types of control structure, derived from structured programming: Sequences of instructions Selection of alternative instructions (or groups of instructions) Iteration (repetition) of instructions (or groups of instructions) The Sequence Structure Directs computer to process program instructions in a particular order Set of step-by-step instructions that accomplish a task I154-1-A Peter Lo I154-1-A Peter Lo The Selection Structure The Iteration Structure Also called the Decision Structure, Makes a decision and then takes appropriate action based on that decision Used every time you drive your car and approach an intersection Directs computer to repeat one or more instructions until some condition is met Also referred to as a Loop, Repeating or Iteration I154-1-A Peter Lo I154-1-A Peter Lo

8 If Then Else Block Decision If Then Else / Select Case I154-1-A Peter Lo Programs need to do different things in response to different conditions. The If...Then statement allows you to evaluate a condition and to then run different sections of code based on the results of that condition. Will be executed if condition is True Will be executed if condition is False If condition Then action1 Else action2 End If If condition Then action1 End If Statement 2 Statement 3 Regardless of whether the condition in the If statement is True or False, these statements will be executed I154-1-A Peter Lo Workflow for If Then Else Block ElseIf Block I154-1-A Peter Lo An extension of the If block allows for more than two possible alternatives with the inclusion of ElseIf clauses. There is no space between the word "Else" and "If and only one "End If" is required. If condition1 Then action1 ElseIf condition2 Then action2 ElseIf condition3 Then action3 Else action4 End If I154-1-A Peter Lo

9 Simplified Nested If Statement Select Case Terminology When one If block is contained inside another If block, the structure is referred to as nested If blocks. Care should be taken to make If blocks easy to understand. If cond1 Then If cond1 And cond2 Then If cond2 Then action action End If End If End If Nested If Less Confusing I154-1-A Peter Lo A decision-making structure that simplifies choosing among several actions. Avoids complex nested If constructs. If blocks make decisions based on the truth value of a condition; Select Case choices are determined by the value of an expression called a Selector. Select Case Selector Selector Case Value1 Action1 Case Value2 to Value3 Action 2 Case Else Action of last resort End Select Value Lists I154-1-A Peter Lo Workflow for Select Case Block Rules for Select Case Case Else (and its action) is optional Each value list contains one or more of the following types of items separated by commas: A literal; A variable; An expression; An inequality sign preceded by Is and followed by a literal, variable, or expression; A range expressed in the form a To b, where a and b are literals, variables, or expressions. I154-1-A Peter Lo I154-1-A Peter Lo

10 Do Loop Type of Do Loop Explanation Example Iteration Pre Test Loop / Pro Test Loop / For Loop Do While Loop Do Until... Loop Do... Loop While Do... Loop Until The Do While... Loop evaluates the condition, and if the condition is true, then it evaluates the statements following the condition. When it has finished doing this, it evaluates the condition again and if the condition is true, it evaluates the statements again. It continues repeating this process until the condition is false. The Do Until... Loop is similar to the Do While... Loop except it keeps evaluating the statements until the condition is true rather than while it is true. The Do... Loop While evaluates the statements only once. It then evaluates the condition, and if the condition is true, evaluates the statements again. This process continues until the condition is false. Similar to Do... Loop While except that it evaluates the statements until the condition is true. Do While condition statements Loop Do Until condition statements Loop Do statements Loop While condition Do statements Loop Until condition I154-1-A Peter Lo I154-1-A Peter Lo Pre Test Loops Workflow for Pre Test Loop A loop is one of the most important structures in programming. Used to repeat a sequence of statements a number of times. The Do loop repeats a sequence of statements either as long as or until a certain condition is true. Do While / Until condition statement(s) Loop Condition is tested. If it is True, the loop is run. If it is False, the statements following the Loop statement are executed. These statements are inside the body of the loop and are run if the condition above is True. I154-1-A Peter Lo I154-1-A Peter Lo

11 Example for Pre Test Loop Post Test Loop I154-1-A Peter Lo A Do statement precedes the sequence of statements, and a Loop statement follows the sequence of statements. The condition, preceded by either the word While or the word Until, follows the word Do or the word Loop. Be careful to avoid infinite loops loops that never end. VB.NET allows for the use of either the While keyword or the Until keyword at the top or the bottom of a loop. Do statement(s) Loop Until / While condition Loop is executed once and then the condition is tested. If it is False, the loop is run again. If it is True, the statements I154-1-A Peter Lo following the Loop statement are executed. Workflow for Post Test Loop Example for Post Test Loop I154-1-A Peter Lo I154-1-A Peter Lo

12 For Next Loops You can use a For...Next loop when a section of code is to be executed an exact number of times For Next loops enable you to evaluate a sequence of statements multiple times. For and Next statements must be paired and a counter is used to control the loop Start, Stop, and Step values Consider a loop beginning with For i = m To n Step s. The loop will be executed exactly once if m equals n no matter what value s has. The loop will not be executed at all if m is greater than n and s is positive, or if m is less than n and s is negative. I154-1-A Peter Lo I154-1-A Peter Lo Altering the Control Variable Example for For Next Loop The value of the control variable should not be altered within the body of the loop; doing so might cause the loop to repeat indefinitely or have an unpredictable number of repetitions. Non-integer step values can lead to round-off errors with the result that the loop is not executed the intended number of times. I154-1-A Peter Lo I154-1-A Peter Lo

13 Generating Random Integers Creating Random Number The Random Function Pseudo-random number generator: a device that produces a sequence of numbers that meets certain statistical requirements for randomness Random object: represents a pseudo-random number generator Random.Next method: Generates a random integer Can specify a minimum and maximum value I154-1-A Peter Lo I154-1-A Peter Lo How to Generate a Random Number? I154-1-A Peter Lo